Reply to "Piston damage found...."

Angelo

Since your motor is apart, now is the time to address the problems and improve the durability

The 351C 4V has 2 weaknesses.

(1) There was a problem with the quality control of the nitriding process of the production 4V valves. Like many valves the 4V valves are a two piece design, the stems are welded to the valve heads. Over the last 4 decades many 351C owners have experienced the misfortune of having one of their 4V valves drop its head while the motor is running, resulting in devastating damage to the motor. The valve head breaks off where it is welded to the stem. It has happened to completely stock motors, mildly modified motors and extensively modified motors too. The damage can occur while the motor is idling in the driveway, cruising on the road or wicked fully open (WFO). There is no way to predict if or when it will happen. The fact that a motor has run for 4 decades using the original valves is no guarantee it wont drop a valve tomorrow. If your 351C 4V is still equipped with the original Ford valves, it is a ticking time bomb.

(2) The production connecting rod nuts were the weakest link in the 351C reciprocating assembly. The threads will pull out of the nut when the motor is run hard and the result is major carnage. An easy upgrade is to simply replace the nuts with parts from ARP, #300-8371. The connecting rod bolt can be re-used. If you replace the bolts the big-ends of the rods will have to be re-sized. Leaving the bolts in place and replacing only the nuts will avoid having to have the rods re-sized. The nuts truly are the problem

Yes, replace the pistons with a set of Forged full round skirt flat top pistons. Possible manufacturers include (A) Arias #1210020 (B) BRC Performance #31404 (C) Ross #80556. You'll need new rings as well. I'd have to see, feel and measure the cylinders before I could tell you if a simple honing would clean the cylinders up for the new rings, or if the block needs to be bored. New pistons means you MUST remove the ridge at the top of the cylinders. If any of the rings ride higher in the cylinder than they did with the old pistons, they will break when they hit the ridges.

Replace the crankshaft main journal bearings and rod journal bearing with Clevite 77 bearings, use the uppers from two sets of main journal bearings so that your main journal bearings are fully grooved, 360 degrees. Replace the camshaft timing set with a new full roller billet timing set from Roll Master. The crankshaft rear main seal is a rope seal, replace it with a neoprene seal, this requires pulling a small pin from the seal groove in the rear main bearing cap and filling the pin hole with a dab of sealant. The harmonic dampener is over 35 years old, the rubber bonding the outer ring to the inner hub cannot be trusted, please have that dampener rebuilt or replaced. I would like to suggest the dampener from a 1977 - 1981 351M or 400 truck motor as a replacement.

Have the reciprocating assembly dynamically balanced before reassembly.

If your motor still has a breaker point ignition now is the time to upgrade to a breakerless system.

You should pull the lifters & cam & inspect them for worn lifter faces and worn camshaft lobe noses. Each lifter MUST go back into the bore it cam out of. If you re-use the cam, I suggest you install it 4 degrees advanced. The cam timing in the '72-'74 Cobra Jet motors was retarded 4 degrees. Advancing it 4 degrees brings it back to 1971 specs. The Roll Master timing set should have a multi-index crank sprocket which will allow you to do this. The camshaft should be "degreed" during installation (to insure accurate valve timing).

Is there anyway I can talk you into a high pressure oil pump spring, restrictors for the camshaft bearings and push-rods with 0.040" restrictors in the tips? Ideally your hot oil pressure should be at least 70 psi at 2000 rpm and above, 50 to 69 psi hot oil pressure at 2000 rpm and above is acceptable only on a temporary basis, I don't recommend running the motor hard if that's all the pressure you have. Don't run the motor at all with hot oil pressure less than 50 psi. The restricted push rods will control the amount of oil flowing to the valve train with hydraulic lifters. If you upgrade the oil pump spring you must start using a high pressure oil filter too, because on cold starts the oil pressure will be about 130 psi.

The pic below shows the carnage created by a dropped valve head.

-G